CBOLINESTERASES FROM THE COMMON OYSTER (CRASSOSTREA-GIGAS) - EVIDENCEFOR THE PRESENCE OF A SOLUBLE ACETYLCHOLINESTERASE INSENSITIVE TO ORGANOPHOSPHATE AND CARBAMATE INHIBITORS

Marine bivalves such as oysters and mussels are widely used as bioindi cators of contamination in the monitoring of pollutant effects, As fil ter feeders, these species are known to be good general indicators of chemical contamination. However, the efficient use of decreased acetyl cholinesterase activity in the oyster as a biomarker of exposure to ne urotoxic compounds requires a definition of the different types of cho linesterases coexisting in this mollusk, This study reports the partia l purification, separation and characterization of two cholinesterases extracted from the oyster Crassostrea gigas, Differences in apparent molecular weight, type of glycosylation and hydrophobicity, and sensit ivity to inhibitors suggest that they are encoded by two different gen es, 'A' cholinesterase (apparent molecular weight 200 kDa) is anchored to the membrane via a glycolipid, is not glycosylated but sensitive t o organophosphate and carbamate inhibitors, 'B' cholinesterase (molecu lar weight 330 kDa) is hydrophilic, glycosylated and highly resistant to organophosphate and carbamate inhibitors, The kinetic properties of these two cholinesterases were compared with those of other invertebr ate cholinesterases, The presence of a cholinesterase insensitive to i nsecticides suggests that a significant improvement in the use of oyst er cholinesterases as biomarkers of pollutant effects could be achieve d by simple separation of the two forms. (C) 1997 Federation of Europe an Biochemical Societies.